For a variety of reasons, it is desirable to supply fluids, such as electrolytes, to a patient or to collect physiological fluids from a patient in various settings including hospitals, nursing homes, private homes, or wheel chairs. For example, there are many instances of patient treatment where it is necessary to collect and determine, at all times, the accurate amount of expelled body fluids, such as urine, that is being released by the patient. It is, in fact, conventional in hospitals to collect urine from certain patients to measure and monitor urine output over time. This is routinely done for post-operative patients as well as those with urology disorders where, for example, urine output is directly related to renal function. This type of procedure for collecting, measuring and monitoring urine takes on added importance in some cases because sudden changes in urine flow, which can occur at any time, can indicate that there is a deteriorating clinical condition in the patient. Changes in urine output have also been correlated with changes in cardiac output.
The collection of urine and measurement of urine output (i.e., volume per unit time) are typically accomplished by first catheterizing the patient. In this procedure, the catheter is passed through the urethra of the patient into the bladder. The other end of the catheter is connected to a rigid collection container or a flexible vinyl drainage bag through a length of flexible tubing attached to a barbed fluid inlet port on the container. Typically the container is supported below the patient and from the patient's bed or other support system, such as a wheel chair, and urine drains by gravity from the patient through the flexible tubing and into the collection device. For patients who are mobile, this collection device is called a leg bag (flexible container), and for patients in a hospital bed it is called a urine collection device (flexible or rigid container). Hospital bed containers are usually 2,000 ml in capacity and leg bags are typically 1,000 ml, 800 ml, 700 ml, or even smaller. The measurement of container fill volume and urine output are typically accomplished by periodically draining the contents of the container into a graduated cylinder and manually recording the volume collected and the time it was collected. The urine output is then manually calculated and manually entered into the patient's record.
In addition to monitoring urine output as a function of time, the caregiver must monitor the collection container total volume to make sure it does not fill to capacity. This event can occur at unpredicted intervals and someone must empty the container before it can fill once again with urine. Further, patients can sometimes obstruct the flow of urine into the container by lying on and possibly crimping the drain tube. In this case, no urine appears in the container after an expected time period. Both a filled container and blocked input tube can cause urine backup into the bladder and a backup condition can have a deleterious effect on the patient's health. Also, the urine can spill onto the patient's bed linen and potentially cause/worsen various skin problems associated with being bedridden. For all the above reasons, caregivers must monitor the fill level in the collection container over time to make sure it does not overfill or is not properly filling. This manual process is time consuming (i.e., costly) and could also lead to problems associated with handling of urine, which is a biohazard.
U.S. Patent Publication No. 2006/0229515 describes a device for continuously and automatically monitoring the fluid level in collection and delivery containers. A disposable sensor is placed inside the container to measure fluid fill level. A reusable electronic device is attached to the outside of the container to continuously record sensor changes and to wirelessly transmit fill level information to external receiver/data processor/display devices. A connection device through the container wall allows the external electronic device to interface with the internal sensor. The device helps save time, minimize urine backup and also reduce the amount of caregiver-patient urine contact.
An advantage of the device described in U.S. Patent Publication No. 2006/0229515 is that the container could have a variable cross-sectional area typical of flexible, low-cost vinyl bags used in the medical industry. It is desirable to improve the accuracy of fluid level measurements, especially for urine collection devices used in the hospital's intensive care unit (ICU) where accurate initial urine flow rates are considered much more important. It is also desirable to improve measurement accuracy at low container fill volumes.